Method for determining optimized radio-frequency pulse shapes for selective excitation in magnetic resonance spectroscopy and imaging

Abstract

In magnetic resonance spectroscopy and imaging, it is usually necessary to obtain spectra only from desired, localized regions of an examination subject. This is accomplished by subjecting the examination subject to a selective radio-frequency (RF) pulse. A method for optimizing the pulse shape of such a radio-frequency pulse includes the steps of exciting a spin system with a frequency-selective radio-frequency pulse, reading out the resulting echo signal, cutting off high-frequency signal components of the echo signal using a filter, and employing the filtered echo signal as the optimized radio-frequency pulse shape.

I claim as my invention: 
     
       1. A method for determining an optimized radio-frequency pulse shape for selective excitation of a spin system, comprising the steps of: (a) producing the effect of exciting a spin system by a frequency-selective radio frequency pulse;   (b) producing the effect of reading out an echo signal having high-frequency signal parts arising from step (a);   (c) cutting off said high-frequency signal parts of said echo signal with a filter to obtain a filtered echo signal; and   (d) employing said filtered echo signal as an optimized radio-frequency pulse shape for further excitation of said spin system.   
     
     
       2. A method as claimed in claim 1 wherein step (a) is further defined by physically exciting said spin system with a real frequency-selective radio-frequency pulse and wherein step (b) is further defined by undertaking an actual read-out of the echo signal resulting from said radio-frequency pulse. 
     
     
       3. A method as claimed in claim 2 wherein step (b) is further defined by reading-out said echo signal under the influence of a gradient in order to obtain a gradient echo. 
     
     
       4. A method as claimed in claim 1 wherein (a) is further defined by calculating the effect of excitation of said spin system by a frequency-selective radio frequency pulse by simulation calculation, and wherein step (b) is further defined by calculating the echo signal arising from the simulated calculation of step (a) by further simulation calculation. 
     
     
       5. A method as claimed in claim 1 wherein steps (a) and (d) are further defined by using a radio-frequency pulse in step (a) for optimization having a larger flip angle than subsequent radio-frequency pulses used after optimization in step (d). 
     
     
       6. A method as claimed in claim 1 wherein step (a) is further defined by using a sinc pulse as said frequency-selective radio-frequency pulse. 
     
     
       7. A method as claimed in claim 1 wherein step (c) is further defined by cutting off said high-frequency signal parts using a Hamming filter.